[Make-wifi-fast] Fwd: [PATCH] mac80211: prevent skb/txq mismatch

Dave Taht dave.taht at gmail.com
Thu Jan 12 13:44:12 EST 2017

yea! (I think)

---------- Forwarded message ----------
From: Michal Kazior <michal.kazior at tieto.com>
Date: Thu, Jan 12, 2017 at 6:28 AM
Subject: [PATCH] mac80211: prevent skb/txq mismatch
To: johannes at sipsolutions.net
Cc: linux-wireless at vger.kernel.org, greearb at candelatech.com,
mohammed at qti.qualcomm.com, Michal Kazior <michal.kazior at tieto.com>

Station structure is considered as not uploaded
(to driver) until drv_sta_state() finishes. This
call is however done after the structure is
attached to mac80211 internal lists and hashes.
This means mac80211 can lookup (and use) station
structure before it is uploaded to a driver.

If this happens (structure exists, but
sta->uploaded is false) fast_tx path can still be
taken. Deep in the fastpath call the sta->uploaded
is checked against to derive "pubsta" argument for
ieee80211_get_txq(). If sta->uploaded is false
(and sta is actually non-NULL) ieee80211_get_txq()
effectively downgraded to vif->txq.

At first glance this may look innocent but coerces
mac80211 into a state that is almost guaranteed
(codel may drop offending skb) to crash because a
station-oriented skb gets queued up on
vif-oriented txq. The ieee80211_tx_dequeue() ends
up looking at info->control.flags and tries to use
txq->sta which in the fail case is NULL.

It's probably pointless to pretend one can
downgrade skb from sta-txq to vif-txq.

Only drivers using wake_tx_queue were affected.

Example crash dump before fix:

 Unable to handle kernel paging request at virtual address ffffe26c
 PC is at ieee80211_tx_dequeue+0x204/0x690 [mac80211]
 [<bf4252a4>] (ieee80211_tx_dequeue [mac80211]) from
 [<bf4b1388>] (ath10k_mac_tx_push_txq+0x54/0x1c0 [ath10k_core])
 [<bf4b1388>] (ath10k_mac_tx_push_txq [ath10k_core]) from
 [<bf4bdfbc>] (ath10k_htt_txrx_compl_task+0xd78/0x11d0 [ath10k_core])
 [<bf4bdfbc>] (ath10k_htt_txrx_compl_task [ath10k_core])
 [<bf51c5a4>] (ath10k_pci_napi_poll+0x54/0xe8 [ath10k_pci])
 [<bf51c5a4>] (ath10k_pci_napi_poll [ath10k_pci]) from
 [<c0572e90>] (net_rx_action+0xac/0x160)

Reported-by: Mohammed Shafi Shajakhan <mohammed at qti.qualcomm.com>
Signed-off-by: Michal Kazior <michal.kazior at tieto.com>
 net/mac80211/tx.c | 17 +++++++----------
 1 file changed, 7 insertions(+), 10 deletions(-)

diff --git a/net/mac80211/tx.c b/net/mac80211/tx.c
index 4dea18be385c..c77fcf83d004 100644
--- a/net/mac80211/tx.c
+++ b/net/mac80211/tx.c
@@ -1244,13 +1244,16 @@ ieee80211_tx_prepare(struct
ieee80211_sub_if_data *sdata,

 static struct txq_info *ieee80211_get_txq(struct ieee80211_local *local,
                                          struct ieee80211_vif *vif,
-                                         struct ieee80211_sta *pubsta,
+                                         struct sta_info *sta,
                                          struct sk_buff *skb)
        struct ieee80211_hdr *hdr = (struct ieee80211_hdr *) skb->data;
        struct ieee80211_tx_info *info = IEEE80211_SKB_CB(skb);
        struct ieee80211_txq *txq = NULL;

+       if (sta && !sta->uploaded)
+               return NULL;
        if ((info->flags & IEEE80211_TX_CTL_SEND_AFTER_DTIM) ||
            (info->control.flags & IEEE80211_TX_CTRL_PS_RESPONSE))
                return NULL;
@@ -1258,10 +1261,10 @@ static struct txq_info
*ieee80211_get_txq(struct ieee80211_local *local,
        if (!ieee80211_is_data(hdr->frame_control))
                return NULL;

-       if (pubsta) {
+       if (sta) {
                u8 tid = skb->priority & IEEE80211_QOS_CTL_TID_MASK;

-               txq = pubsta->txq[tid];
+               txq = sta->sta.txq[tid];
        } else if (vif) {
                txq = vif->txq;
@@ -1504,23 +1507,17 @@ static bool ieee80211_queue_skb(struct
ieee80211_local *local,
        struct fq *fq = &local->fq;
        struct ieee80211_vif *vif;
        struct txq_info *txqi;
-       struct ieee80211_sta *pubsta;

        if (!local->ops->wake_tx_queue ||
            sdata->vif.type == NL80211_IFTYPE_MONITOR)
                return false;

-       if (sta && sta->uploaded)
-               pubsta = &sta->sta;
-       else
-               pubsta = NULL;
        if (sdata->vif.type == NL80211_IFTYPE_AP_VLAN)
                sdata = container_of(sdata->bss,
                                     struct ieee80211_sub_if_data, u.ap);

        vif = &sdata->vif;
-       txqi = ieee80211_get_txq(local, vif, pubsta, skb);
+       txqi = ieee80211_get_txq(local, vif, sta, skb);

        if (!txqi)
                return false;

Dave Täht
Let's go make home routers and wifi faster! With better software!

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